el natural questions!

I posted the start of a new journal... it's currently in the 'gallery' forum... oops... i'm hoping a mod will move it to the journal forum - hint hint!!

Anyway, I also have many many questions:

1 - Do i need to strip my tank down completely? I've read about using frozen soil inserts... if i use these with root fert tabs... will that be enough to get the plants going? Basically, is a full soil 'layer' essential?

2 - i've got pea-grade standard aquarium gravel what are the odds that this will stagnate? I REALLY don't want to go through that again.

3 - I live in a flat and don't have access to topsoil have any UK members here used any 'off the shelf' soil products with success? By that i mean commerical soil / compost for plants - not expensive aquarium products like laterite.,

Hi,
Laterite is overated and is no longer in vogue. If you want to avoid the cost of enriched aquarium substrates you can still use a mixture of regular compost (baked or allowed to sit in water for a few weeks prior) and sand, but this would mean a stripdown. You could use something like Akadama as describe in this sticky->http://ukaps.org/forum/viewtopic.php?f=17&t=741
You can prepare the substrate and then add it in stages.

At the end of the day though these are aquatic plants which feed predominantly via the leaf, therefore sufficient water column dosing will do the trick regardless of substrate choice.

Hi,
"Root feeder plants" is another chapter in the book of plant keeping mythology. Swords are among the most voracious of water column feeders. Crypts are not far behind and are world class CO2 and nitrate hogs. Just look at the size of their leaves. Why would an aquatic plant go through all the trouble of having big long wide aquatic leaves and then choose to feed predominantly from the roots instead? Something to ponder.

Yes, but many plants do this with small leaf structures including the tiniest such as glosso or HC. This is accomplished by simply having a high density of chloroplasts within the leaf structure, not by size. Also, the large leaf structure has to be manufactured, supported and maintained by nutrient uptake so the efficiency would be poor if there was predominant root uptake. The photosynthesis reaction chambers are in the leaf so that the distance the nutrient has to travel is measured in terms of millimeters whereas it can be many centimeters when transported from the roots.

Having both a nutritious substrate and water column nutrient availability is ideal as it reduces the pressures of nutrient supply from either location, however you can quickly grow gigantic swords and crypts in nothing but inert sand if you provide sufficient water column dosing. It's not as easy to do it the other way round though.

In emersed plants large leaves generally evolve to collect as much sunlight as possible (along with a range of other adaptations to the cellular structure of the leaf and alterations to the photosynthetic pigments) in calm (so the leaves aren't damamged) dark places such as forest floors. Sword plants also have emersed leaves that are rather similar to their submersed leaves in most species which suggests that they spend a lot of their natural life emersed and are evolved to optimise that. Submersed leaves are their way to make the best of a bad situation and they perform the functions well enough to be successful.

That does not mean that their leaves cannot absorb nutrients as foliar feeds of ordinary garden plants are one of the most efficent ways of getting nutrients into plant tissues quickly. They do this effectively despite not having evolved to do this, indeed only some epiphitic and carnivorous plants, as far as I know, have specifically evolved to maximise this foliar method of gaining nutrients. As Clive says this notion of 'root feeders' is a misconception.

The fact is that even if you have a tank with a nutritious substrate some of those nutrients will diffuse into the water column anyway so you could never say that they were only gaining nutrition through the roots unless the rest of the plant was out of water!!!

One more quick thought about roots. They serve other functions for aquatic plants besides nutrient uptake. Firstly, the environments in which many of these heavily rooted plants are found are sometimes subject to turbulent flow due flooding and disturbances especially during the transition to the wet season when the plants go from emmersed (terrestrial) growth to submerged mode. Heavy root structure allows the plants to "hang on" during the transitional period as well as in the steady state conditions if they are in a riverine or tributary system rather than a low flow (lake/pond) system. Secondly, there is a symbiotic relationship between the plants and the aerobic bacteria in the sediment. In order to nitrify the decay in the sediment, i.e to change NH4 to NO3 the bacterias that perform this function require oxygen as they are aerobic. The plants transfer oxygen from the reaction chambers in the leaf to the root structure where the oxygen is released into the sediment thereby helping these nitrifying bacteria to survive, to detoxify the sediment and as Ed mentions, to release nitrates into the water column for feeding by the leaves. Crypts and swords are particularly good at this due to their extensive root structure as well as the well developed hollow canals in their leaves and stems (called Lacunae) which facilitate oxygen transfer to the root zone.

A large root structure also traps organic debris and allows, within the oxygenated zone microorganisms to feed, and for the debris to decay. This generates CO2, which the plant can then use. Many plants have the ability to sequester CO2 and by an overwhelming margin, the ability of a plant to sequester CO2 and to feed from sedimentary CO2 is correlated to having a large root structure.

Here is an example of the well developed transport system of a sword. You can see the bulging main canals converging into the stem below which have a hard external structure for protection and a spongy interior in which the hollow spaces of the spongy tissue facilitate oxygen transport to the roots. Large root structures therefore require large leaf structure to feed and to support the roots. The area in the sediment surrounding a sword is usually well aerated and has a high aerobic bacteria count. This makes the amazon sword an excellent choice for cycling a tank and for reducing the possibility of stagnant anaerobic sediment, but water column dosing is just as critical as it is for stem plants.

I read a thread on the forum on tom Barr's site where he mentioned the 'walsted method' and went on to say that even in low-tech tanks a light dosing regieme of flourish excel and some dry ferts would have a significant effect on plant growth... but that it would still be slower than in the high light / c02 tank (of course).

The dry ferts are exactly the same as those that would be used in the high tech tank. Barr recommends to add about 1/8 teaspoon of KNO3 and 1/32 teaspoon KH2PO4 per 20 USgallon once a week or two. You may also dose traces such as CSM+B. It may be easier to just make life simpler though by using Tropica TPN+ once a week. This is an all in one and you would avoid the hassle of measuring out powders.

The dry ferts are exactly the same as those that would be used in the high tech tank. Barr recommends to add about 1/8 teaspoon of KNO3 and 1/32 teaspoon KH2PO4 per 20 USgallon once a week or two. You may also dose traces such as CSM+B. It may be easier to just make life simpler though by using Tropica TPN+ once a week. This is an all in one and you would avoid the hassle of measuring out powders.

I'm afriad I have to disagree that the idea of aquatic plants that are root feeders are a myth. My evidence, the simple fact that if you take a so called root feeder that has nice big leaves and cut the roots right back you will get a LOT of die back of the leaves. Your hypothesis that the reason they will grow fine in plain old sand/gravel with only water column dosing is missing the simple fact that much of the ferts added to the water column will in fact also reach the roots, through currents such as convection currents etc. As such, the so called root feeders such as echinodorus and cryptocoryne do indeed feed through their roots, as well as their leaves, and can recover far more easily from loss of leaves than they can from loss of roots. Why else do you think that pruning the roots helps to slow the growth on some of the faster growing species?

Stem plants on the other hand you can cut the roots off completely (in other words, take a cutting) and they will continue to grow quite happily and grow new roots, as the majority of stem plants get the majority of their nutrients directly from the water column.

Hi,
I've never experienced die back of sword leaves after root pruning, ever. Coincidentally my water column is always rich in nutrients and high in CO2. My contention is not that swords don't feed from the roots, but that they don't feed preferentially from the roots any more than other plants. While there is little doubt that more roots allow more root feeding, swords leaf feed with the best of any stem plant. The other thing that many don't consider is that aquatic plants live as terrestrial plants for half the year during the dry season when they are not submerged, at which time root feeding is imperative.

When planting a sword, or crypt it is a standard practice to trim the roots right back prior to planting. In a nutrient rich water column, with high CO2 these plants are among the first to to start producing leaves, even with the roots cut back. This can only be accomplished by having efficient leaf feeding.

Furthermore, stem plants also feed through their roots in exactly the same way as crypts and swords. Root feeding is slow and inefficient when compared to leaf feeding however. The higher the lighting the more clearly this can be demonstrated. The physical structure of all aquatic plants in their submerged mode are optimized to take advantage of whatever nutrients are present in the water column. They accomplish this by eliminating the cuticle, which the waxy waterproof coating on the leaf. This allows water to penetrate the membranes easily. In this way nutrients and gases such as CO2 and Oxygen can move across the membrane more easily in water. There are many other physiological changes that occur on the exterior and interior. These changes occur for crypts and swords in exactly the same way as they do for stem plants.

If you observe in the photo above you'll see that the leaf exhibiting gaseous exchange. That means oxygen is released and CO2 is absorbed across the leaf membrane. If a CO2 molecule can find it's way into the leaf membrane do you think it would be difficult for NO3 and PO4 molecules to find their way across the membrane as well? And why would the leaf reject these critical components and wait for the much slower process of nutrient diffusion into the sediment? Also, current flow in the substrate moves both ways so that nutrients migrate out of the sediment as easily as migrating into the sediment.

The propaganda of preferential root feeding developed in part because over the past few decades, before water column dosing was made a priority most have had very lean dosing in the water. Because the extensive root structure of the swords and crypts they can do a better job in a lean water column environment than plants with a less extensive root system. This led to the belief that these plants were predominantly root feeders. With the advent of high energy lighting and rich water column dosing it is seen that this label is false. If you exhibit dieback of sword leaves after root pruning that may imply that your water column is lean and therefore cutting the roots shuts the other avenue of feeding for the plant.

Hi,
"Root feeder plants" is another chapter in the book of plant keeping mythology.

Click to expand...

This is the part of your post that I was disagreeing with, not that swords and cryptocoryne plants feed from the water column. You yourself have already stated that you were not claimning that sword don't feed from the roots. Which was the basis of my disagreement. Root feeding plants is not a myth, the myth is rather that these plants feed only from the roots.

As to cutting back the roots, cut the roots of a cryptocorne or sword plant far enough (more so in the case of crytocoryne plants) and you will get SOME die back, even in the presence of high levels of nutrients in the water column. They will however grow back faster in these conditions. You can not prove that the plants are mainly feeding via their stems and leaves from the water column, as you have already agreed nutrients pass both ways from substrate to water column.

As to gaseous transfer across the leaf membrane, this is achieved using stomata, the size of which could indeed limit the transfer of gasses to CO2 and O2, this is the very nature of osmosis as "diffusion across a SELECTIVELY permeable membrane". Reverse osmosis systems are a perfect example of this, where nothing larger than a water molecule is able to cross the membrane. However plants do indeed take in nutrients via the leaves, in both aquatic plants and terrestrial ones.

I am also quite sure that your planted tanks have a plant substrate in them, which will be providing nutrients to the roots, along with those provided by diffusion and currents through your substrated, which will in part account for some of your success with these plants.

We can however agree that the idea that plants feed exclusively, or preferentially, by the roots IS a myth. However, I have found that these types of plants do seem to do better with some form of substrate fertilisation. I would also suggest that in cases where the substrate is composed solely of an intert, nutrient poor, aggregate that substrate fertilisers are even more useful, in effect helping to turn your substrate into more of a planted tank substrate.

Incidentally, I would not say that laterite is useless. It's just another form of clay, as are most of the planted tank substrates. I would however say that it does best when combined with other substrates (peat etc). When I first started keeping a planted tank there were not the choices that there are today, and the choices that were available were even more expensive than they are now. As such I chose to use laterite, combined with peat, activated charcoal and a 1-2mm silica grit (rounded granuals), and to enrich this further using root tabs and balls. Ever since I have seen phenominal growth in ALL plants, including so called slow growers. I have even succesfully grown plants that require high light in a low light setup. I had to stop growing larger swords, purely because they just got too big too quickly! I would not however ever suggest or advocate the use of 'root' fertilisers in isolation, I quite agree that water column dosing is as, if not more so, important. If 'root' fertilisation was completely pointless, then there would be absolutely no market for, or need to use, plant substrates or even DIY ones such as Akadama. I just wish that I had had these choices when I set up my planted aquarium.

Hi,
"Root feeder plants" is another chapter in the book of plant keeping mythology.

Click to expand...

If 'root' fertilisation was completely pointless, then there would be absolutely no market for, or need to use, plant substrates or even DIY ones such as Akadama.

Ade

Click to expand...

I have to admit i do agree that if so called 'root feeding' plants did just as well without the mess and expense of rich substrates then people like amano and barr would have told us to not worry about it by now... as it is, people agonise over substrate a lot!

But i must also admit to not being as educated as either of you two on the associated issues!

I'll repeat that the issue is not whether plants feed from the roots. The issue is whether plants feed preferentially from the roots. That is what the term "root feeder" is meant to imply. This is the basis of the myth. The question was whether you needed to do something special for "root feeders" as opposed to the stems. The answer is no. If you have a nutritious substrate both stem and rosette plants will benefit from the substrate. Substrate feeding helps reduce the pressures of water column feeding for all plants that are anchored to the substrate. Having both is better than having only one. The advantage is not limited to swords but to all plants rooted in the substrate.

If you have a plant, rosette or stem, under very high lighting and if it is in a nutritious substrate with zero water column dosing you will soon see that the plant will fall into deficiency and the result will be algae. It doesn't matter how nutritious that substrate is, the roots cannot uptake nutrients fast enough to satisfy the growth requirements of the plant under that lighting condition. Yes there will be leaching into the water column but not quickly enough. We see this everyday and inevitable, water column dosing resolves the issue.

If on the other hand you change the conditions of the test and replace that substrate with an inert substrate such as sand and introduce water column dosing the plant can uptake the nutrients in the water column to completely avoid deficiency. The amount that diffuses into the inert substrate will not be a significant quantity as compared to the uptake across the leaf.

The higher the light the greater the disparity in the nutrient uptake between root and leaf. In a lower light environment this disparity is not demonstrated as easily because the demands of growth are much less as a direct result of the lower energy.

If you cut a sword into the crown you will do damage to the plant. When I cut the swords back I cut them to with a few centimeters of the crown and replant. I do this even with new plants that come from a shop emersed. The plant continues on and has new growth within 24-48 hours. There is therefore sufficient proof to conclude that leaf feeding is at play.

Submerged aquatic macrophytes do not share the same characteristics as an RO filter. This would be self defeating as the nutrient, gaseous and organic product exchange within the water column is difficult enough. A better comparison would be a gas permeable soft contact lens. In the general course of events SAMs release carbohydrates and waste products into the water column. These organic molecules are hundreds or even thousands of times larger than a CO2 or and nutrient molecule. Therefore if these large molecules can find their way across the leaf membrane then nutrients will not have any difficulty doing the same. The effect is of diffusion, not filtration. Osmotic forces are used to accelerate uptake across the membrane so the filtration analogy is not really appropriate.

Laterite is useless within the context of which it was marketed many years ago, as an indispensable form of iron to be taken up by the roots. Everyone rushed out and purchased "laterite balls" or lined the bottom of their tank with laterite powder, when in fact this was unnecessary. I used Kitty litter and peat, so any clay product could be used with equal effect and iron can be transported to where it is needed if dosed from the water column.

The function of the substrate is more widespread than merely how much nutrients can be taken up by the roots. The substrate also acts as a warehouse for bacteria and subsequent nitrification, which affects the entire system. So I'm not trying to say that substrates are unimportant, far from it, but that plants should be segregated in terms of predominant root feeding versus predominant water column feeding is misleading.

I'll repeat that the issue is not whether plants feed from the roots. The issue is whether plants feed preferentially from the roots. That is what the term "root feeder" is meant to imply. This is the basis of the myth. The question was whether you needed to do something special for "root feeders" as opposed to the stems. The answer is no. If you have a nutritious substrate both stem and rosette plants will benefit from the substrate. Substrate feeding helps reduce the pressures of water column feeding for all plants that are anchored to the substrate. Having both is better than having only one. The advantage is not limited to swords but to all plants rooted in the substrate.

If you have a plant, rosette or stem, under very high lighting and if it is in a nutritious substrate with zero water column dosing you will soon see that the plant will fall into deficiency and the result will be algae. It doesn't matter how nutritious that substrate is, the roots cannot uptake nutrients fast enough to satisfy the growth requirements of the plant under that lighting condition. Yes there will be leaching into the water column but not quickly enough. We see this everyday and inevitable, water column dosing resolves the issue.

If on the other hand you change the conditions of the test and replace that substrate with an inert substrate such as sand and introduce water column dosing the plant can uptake the nutrients in the water column to completely avoid deficiency. The amount that diffuses into the inert substrate will not be a significant quantity as compared to the uptake across the leaf.

The higher the light the greater the disparity in the nutrient uptake between root and leaf. In a lower light environment this disparity is not demonstrated as easily because the demands of growth are much less as a direct result of the lower energy.

If you cut a sword into the crown you will do damage to the plant. When I cut the swords back I cut them to with a few centimeters of the crown and replant. I do this even with new plants that come from a shop emersed. The plant continues on and has new growth within 24-48 hours. There is therefore sufficient proof to conclude that leaf feeding is at play.

Submerged aquatic macrophytes do not share the same characteristics as an RO filter. This would be self defeating as the nutrient, gaseous and organic product exchange within the water column is difficult enough. A better comparison would be a gas permeable soft contact lens. In the general course of events SAMs release carbohydrates and waste products into the water column. These organic molecules are hundreds or even thousands of times larger than a CO2 or and nutrient molecule. Therefore if these large molecules can find their way across the leaf membrane then nutrients will not have any difficulty doing the same. The effect is of diffusion, not filtration. Osmotic forces are used to accelerate uptake across the membrane so the filtration analogy is not really appropriate.

Laterite is useless within the context of which it was marketed many years ago, as an indispensable form of iron to be taken up by the roots. Everyone rushed out and purchased "laterite balls" or lined the bottom of their tank with laterite powder, when in fact this was unnecessary. I used Kitty litter and peat, so any clay product could be used with equal effect and iron can be transported to where it is needed if dosed from the water column.

The function of the substrate is more widespread than merely how much nutrients can be taken up by the roots. The substrate also acts as a warehouse for bacteria and subsequent nitrification, which affects the entire system. So I'm not trying to say that substrates are unimportant, far from it, but that plants should be segregated in terms of predominant root feeding versus predominant water column feeding is misleading.

Cheers,

Click to expand...

On balance, though, are there plants that do better with a nutritient rich subsrate than others that can do extremely well with a relatively poor substrate? (given equal water column in each case?)

It would be a really interesting experiment to put this to the test... tank A no ferts at all, tank B substrate only, tank c water column only, tank d both!

The only plants that don't care about the substrate, or can do just as well well with poor substrate are floating plants (and those with rhizomes above the substrate like anubias or ferns). This may seem obvious but what is less obvious is that since floating plants have not interaction with the sediment the soil bacterial colony is lower, and there is a significantly lower level of nitrification. Any rooted plant will do better with a rich substrate, but more importantly perhaps is that the roots of a plant feed and support the bacteria colony in the substrate. That has tremendous implications for us in terms of algae control. A lot of the experiments have already been done showing the importance of substrates from an ecological standpoint.

The difficulty of the tests as Wolfenrook notes is how to avoid "contamination" of one media by the other. In T. Barrs sediment tests, it was necessary to continually draw water away from the test tanks so that any leached water column nutrients were expelled.